Hearing-aid amplifier



I7, 1940. D. BABBITT ETAL HEARING-AID AMPLI r IER Filed Nov. 23, 19:8 3 Sheets-Sheet 1 47 INVENTORS DEAN BABBITT HE I2MANN SCHEIBLEE S ludmmwlzm ATTORNEY DEC. 17,

D. BABBITT ETAL HEARING-AID AMPLIFIER 3 Sheets-Sheet 3 Filed Nov. 23, 1938 s m T N EL 4 m 1 5-. 01 1 6 to 1 6| 8 L 5 m 8 m 5 8 1 DEAN BABBITT HERMANN SCHEIBLER smMWw ATTORNEY Patented Dec. 17, 1940 UNlTED STATES PATENT OFFICE HEARING-AID ANIPLIFIER Application November 23, 1938, Serial No. 241,950

10 Claims.

This invention relates to audiphone microphone amplifiers and it has among its objects improved microphone amplifiers for wearable audiphones, and improved methods for selectively varying the response characteristics of such microphone amplifiers in accordance with the needs of a user. In accordance with the invention audiphone microphone amplifiers, of the type described, for instance, in the United States Patent Re. 19,246 are provided with a self-contained readily detachable exchangeable microphone unit formed of a rigid self-supporting microphone chamber with a carbon granule filling held between a vibratory microphone electrode and a cooperating electrode of opposite polarity combined and arranged so that the microphone unit may be readily mounted on the speech current-energized vibrating structure of the amplifier and may be easily and quickly replaced by another similar microphone unit.

Such improved microphone amplifier arrangement is of particular advantage in connection with the selective fitting of wearable audiphone because the overall response of such audiphone may be readily modified by selectively testing the hearing aid with diiferent, readily exchangeable amplifier microphone units having different response characteristics, and thus determining which amplifier microphone unit gives the individual best hearing.

The foregoing and other objects of the inven tion will be best understood from the following description of exemplifications thereof, reference being had to the accompanying drawings, where- Fig. 1 is a diagrammatic view of a wearable audiphone device embodying an exemplification of the invention;

Fig. 2 is a vertical sectional view of a microphone amplifier exemplifying the invention along line 22 of Fig. 3;

Fig. 3 is a horizontal sectional view along line 3-3 of Fig. 2;

Fig. i is a horizontal sectional view along line 4-4 of Fig. 2;

Fig. 5 is a vertical sectional View along line 5-5 of Fig. 4;

Fig. 6 is a transverse vertical sectional view along line 66 of Fig. 5;

Fig. 7 is a transverse vertical sectional view along line 'l'l of Fig. 5;

Fig. 8 is a perspective view of the microphone unit of the amplifier of Figs. 2 to 7 Fig. 9 is a view similar to Fig. 4 of a portion of a microphone amplifier with a microphone unit of another exemplification of the invention;

Fig. 10 is a perspective view of the microphone unit of Fig. 9;

Fig. 11 is a vertical sectional view of a microphone amplifier illustrating another exemplification of the invention; and

Fig. 12 is a plan view of the amplifier of Fig. 11.

Most of the deafened are very sensitive and seek to conceal their hearing impairment. Accordingly, a satisfactory hearing-aid device for sunplying a deafened person with the large amount of amplified hearing-inducing sound energy must be suitable for comfortable and inconspicuous Wear and must be simple and foolproof in operation so as to free the user from physical as well as mental strains. All the elements of the device must not only be very small and light in weight, but they must be able to respond at high ellicienoy to all important speech frequencies and they must operate satisfactorily under all conditions of use without special attention and frequent reconditioning.

Since the excessive bulk of the batteries and the related accessories make it impossible to use the highly developed electron tube amplifiers in such wearable hearing-aids, many efiorts have been made in the past to devise a small wearable hearing-aid microphone amplifier for supplying the large amplified sound energy output required in a satisfactory hearing-aid.

Such microphone amplifiers consist of a filling of microphonic carbon granules held in a chamber between a vertically positioned vibratory diaphragm electrode and a cooperating electrode of opposite polarity for modulating the output current traversing the granules in accordance with the vibrations imparted to the diaphragm electrode by the speech frequency input currents supplied to the amplifier. Such amplifiers depend for their action on the variation of the contact resistance between a large number of carbon particles. These contact variations are erratic and produce many disturbing effects. Very serious difilculties are also caused by the deterioration of the contact surfaces of the chamber elec trodes, and particularly the surface of the vibratory diaphragm electrode of such amplifiers which become overheated and burned in use. Much trouble is also caused by overmodulation which occurs when vibrations are imparted to some carbon particles with an intensity at which they do not oscillate around a fixed position of equilibrium in continuous contact with each other and the electrodes, but move freely and break their current-carrying contacts causing sparking. Such microphone amplifiers give also a great deal of trouble due to packing or fading when overheating of the carbon granules causes them to bake together and to cut off the output.

Many of these obstacles have been overcome by the now widely used large output hearing-aid microphone amplifiers made in accordance with Reissue Patent 192% of July 17, 1934, in which the electrodes of the microphone chamber are formed of carbon and the movable carbon electrode is actuated by a diaphragm member of a material having much greater stiffness than carbon.

However, even such improved microphone amplifier gives much trouble due to the erratic action between the carbon contact surfaces upon which its operation depends, and the performance of such amplifier deteriorates after it has.

been in use for some period of time.

In order to maintain the hearing-aid in its fullysatisfactory condition, the microphone amplifier must be overhauled, from time to time, and this requires taking apart and reassembling all the operating parts. Heretofore, such reconditioning operations were quite complicated, they required careful and expert manipulations in making critical adjustments, and as a result they were costly and the user had to forego the benefits derived from his hearing-aid for a substantial period of time.

The invention overcomes these difiiculties by combining in a simple, foolproof, efiicient hearing-aid microphone amplifier unit a self-supporting speech current actuated vibratory structure with a self-contained amplifier microphone unit including the diaphragm electrode, the carbon granule filling and the cooperating electrode of opposite polarity arranged to enable easy, simple and quick exchange of one microphone unit with another similar microphone unit without requiring delicate, cumbersome and sensitive adjustment of the cooperating relations between the elements of the microphone unit and the vibratory structure.

It was also long known that the hearing deficiencies of different individuals vary over the range of audible sound frequencies, and that in order to be satisfactory, each hearing-aid should be constructed and arranged to permit selective fitting of each hearing-aid so as to overcome the particular hearing deficiencies of each individual user, in the way described, for instance, in the United States Patent 789,915. Prior to the invention, such selective fitting of amplifier hearing-aids was carried out by means of a testing outfit equipped with a set of several transmitter microphones having different response characteristics, a set of several microphone amplifiers having different response characteristics, a set of different receivers having different response characteristics, and a switching arrangement for successively interconnecting different hearingaid combinations made up of a transmitter microphone, a microphone amplifier, and a receiver, and determining which of the different hearingaid combinations makes the individual hear best.

The improved microphone amplifier of the invention simplifies the problem of selective fitting of hearing-aids because by providing a set of several readily interchangeable amplifier microphone units having diiferent response characteristics, the overall response characteristics of each vhearing-aid combination may be readily modified to fit the particular hearing deficiencies of an individual by successively testing the assembled hearing-aid with different amplifier microphone units and determining with which amplifier microphone unit the hearing-aid fits best the needs of the individual. As a result, the testing outfit may be simplified by providing each testing outfit with only one microphone amplifier for cooperating with a set of several microphone units of different response characteristics so that by mere replacement of one amplifier microphone unit with one of different response characteristics, the overall response characteristics of the hearing-aid may be modified to meet the specific needs of each individual.

The foregoing and other features of the invention will now be explained in connection with an exemplification of a wearable hearing-aid device shown in Fig. 1 comprising a transmitter 20 having microphone electrodes 2|, 22, a control unit 23, a hearing-inducing receiver 21 having an 5 actuating winding 28, and a microphone amplifier unit 3|) having a vibrating structure 3| and an amplifier microphone 33, which are interconnected with a low voltage battery 34 through a cord 35. and the control unit, which for convenience is mounted within the transmitter casing, has a contact rod 38 provided with a contact slider 39 for establishing detachable connection with a rheostat member 40 and a contact strip 4|.

When the contact slider 39 is in the operating position shown in Fig. 1, the two transmitter microphone electrodes 2|, 22 are connected in series with the amplifier winding 32 to the battery 34 for actuating the vibratory structure 3| of the amplifier unit with the speech current energy and produce amplified speech currents in the amplifier microphone 33 connected in series with receiver Winding 28 to the terminals of the battery 34.

The construction of the microphone amplifier unit 30 in accordance with the invention is shown in detail in Figs. 2 to 8.

As shown in Figs. 3 to 5 it comprises an elongated horizontal casing base 43 fitting the top of the battery 34 and having at one end an upwardly projecting terminal block 4d and a cover 45 connected to the base 43 by screws 46, the casing being formed of suitable material, for

instance, a molded synthetic resin compound.

An upwardly projecting supporting wall 41- extending from the casing base 43 has clamped thereto by means of screws 48 one wall of a rectangular frame 49, to which are riveted two T- shaped magnetic core members having angularly r bent pole projections 52 extending into the opening 53 of the frame wall, the end faces of the pole projections 52 lying flush with the outer surface of the frame wall bordering the pole openin 53. Two longitudinal permanent magnet bars 58 held clamped within the frame 49 against the tail pieces of the core members 51 by the spring spacers 59 and energizing coils 6E5 mounted on the projecting pole pieces 52 complete the magnetic core structure of the vibrating unit 3| of the microphone amplifier 3|].

A self-contained amplifier microphone unit 33 shown in detail in Figs. 7 and 8 is detachably mounted opposite the pole pieces 52 of the core, for instance, by two screws 64 secured to the wall of the core frame 49. It comprises a chamber plate 65 of heat conducting material, such as brass, having a central opening within which is firmly fixed a circular microphone chamber wall 66 of a suitable insulating material, such as The transmitter has three terminals 31 synthetic resin. The outer side of the microphone chamber is enclosed by'a carbon disc electrode 19 which is secured, as by soldering, to an annular terminal disc II of brass, for instance, having a threaded circumference engaging a correspondingly threaded portion of the surrounding insulating wall66 of the microphone chamber to permit turning of the terminal disc by means of its grip holes I2 for adjusting the position of the carbon electrode 19 within the microphone chamber.

The opening of the microphone chamber 66 lying opposite the pole pieces 52 is enclosed by a circular diaphragm carbon electrode I4 which is secured, as by soldering, to the center portion of a stiff diaphragm strip 15 of spring material, such as steeLto the opposite side of which is similarly secured a magnetic armatur 16 forming in conjunction with the carbon electrode a rigid central diaphragm portion lying opposite the opening of the microphone chamber 66. free end portions II of the diaphragm strip 15 are widened to increase their rigidity, as shown in detail in Figs. '7 and 8, and are held rigidly clamped by screws I8 to the end portions of the chamber plate 65 so as to hold in the vertical cavity lying between the surfaces of the carbon electrodes I9, 14 a filling of loose carbon balls 89 to vary the contact pressure between the balls in accordance with the vibrations of the carbon diaphragm electrod I4. Shims I9 underlying the diaphragm ends permit adjustment of the operating position of the central diaphragm portion to secure efficient operation of the electromagnetic vibrating unit formed of the armature I6 and the magnetic core members 58 as well as the efiicient operation of the microphone unit by the vibratory motion of the diaphragm carbon electrode I4 in varying the contact pressure of the carbon balls while preventing the balls from falling out from the chamber during the vibrations of the diaphragm.

In order to connect the various elements of the amplifier microphone unit with the elements of the hearing-aid in the way shown in Fig. 1, the casing base 43 is provided with two terminal connector plugs 9I, 92 shaped for detachable engagement with corresponding terminal sleeves of the battery 34, and the projecting terminal block 44 at one end of the base is provided with three terminal connector sockets 93, 94, shaped to permit insertion of the plug pins 96 of a cord plug 91 of the cord 35 in the way shown in Fig. 1.

One end of the serially connected energizing coils 69 of the amplifier unit and the diaphragm electrode I4 are connected through the metallic frame 49 and a spring strip on the casing base to the plug pin 9I engaging one pole of the battery 34. The other pole of the battery leads through plug pin 92 and a connector strip I92 imbedded in the casing base 43 to the terminal block socket 94 which is engaged by the cord plug pin leading to the slider rod 38 of the control unit 23. The other terminal end of the amplifier energizing winding 69 is connected through a contact spring I94 insulatingly mounted on the core frame 49 to a contact strip I95 imbedded in the casing base 43 leading to the terminal socket 93 in the terminal block. And the third terminal socket 95 is connected through a connector strip I96 in the casing base 43 to an upwardly projecting contact spring I 9I shaped to engage the rear side of the metallic terminal disc II. of the stationarymicrophone chamber electrode 19 to complete the circuit from the re- The ceiver winding 28 to the amplifier microphone chamber. An easily detached clamping spring strip I98 of insulating material held by screws I99 on the chamber plate 65 may be utilized to increase the contact pressure with which the contact spring I91 is pressed into engagement with the terminal disc II of the stationary microphone electrode I9.

In order to permit the operation of the microphone amplifier with a large output, a small electrolytic condenser unit I I9 may be mounted within the amplifier casing by attaching its terminal strip III to the frame wall 49 by a screw IIZ to make connection with one diaphragm electrode I4 of the microphone chamber and the insulated condenser lead I I3 of opposite polarity is held by the projecting spring I91 against the terminal disc II of the stationary microphone electrode in the way described in the copending application Serial No. 746,794 filed October 4, 1934, now U. S. Patent No. 2,195,296 issued Jan. 11, 1938.

In manufacturing self-contained detachable amplifier microphone units described above for exchangeable use in connection with the vibrating structure constituting a permanent part of the amplifier unit, each assembled unit is mounted in place on a standard, vibrator structure in the way shown in Fig. 4. Thereafter, while the coils 69 of the vibrating structure are energized by the normal battery current with which such amplifier is operated in the hearing-aid, the mounting of the diaphragm 15 with the diaphragm electrode I4 as well as the stationary chamber electrode I9 is adjusted to secure efficient operation of the amplifier unit. The adjusted microphone unit may then be removed from the standard test vibrator and the same testing operation is performed on each successive unit so that one microphone unit may be readily exchanged for another microphone unit without affecting the operation of the amplifier as a whole.

In the present commercial embodiment of the invention, the microphone chamber of the amplifier unit is made to hold five layers of balls of about 9.5 millimeter and the spacing between the electrode surfaces of the carbon plate I4 of the diaphragm unit 15 and the carbon plate III of the stationary electrode II is adjusted by turning the terminal disc II till the battery current flowing through the microphone chamber in the circuit through the receiver winding 28 is between 90 to 100 milliamperes and the diaphragm adjustment is made to secure during operation an effective magnetic gap of 4 to 5 thousandths of an inch with the normal direct current excitation of the amplifier windings.

Microphone units so adjusted with a standard vibrating structure with which they are designed to operate may be readily exchanged and replaced without disturbing the cooperative relation of the amplifier elements required for their satisfactory operation, and without disturbing the circuit interconnections through which th microphone unit is interconnected to the output circuit and its battery supply.

If required, additional adjustment of the effective operating magnetic gap of an exchangeable microphone unit may be readily provided by attaching two longitudinal springs I I6 to the opposite edges of the chamber plate 65 facing the core assembly, the spring having projecting end portions I I I which are compressed when the microphone unit is clamped to the core frame 49 by means of the clamping screws 64 to permit easy fixing of the effective magnetic gap distance within a predetermined range by screwing in the clamping screws 64 against the pressure of the spacing-springs IIB to a more or less extent.

In Figs.'9 and'is shown a modified form of an exchangeable self-contained microphone unit fora-n amplifier of the invention in which-the cylindrical insulating wall I of the microphone chamber is provided with an external threaded surface engaging a corresponding surface in the central hole; I2I of the microphone chamber plate I22to permit adjustment of theposition of the chamber wall 125 to the supporting plate. Over the chamber opening on thecore side of the chamber plate I22 is mounted aspri-ng diaphragm I23with a magnetic armature I24 and a carbon electrode plate I25 secured to the central portion'of the spring diaphragm as in the amplifier microphone unit of Figs. 7 and 8.

impregnated with a stiffening phenolic condensationproduct, the ends of which are detachably secured to the chamber plate I22 by means of screws I29. With this arrangement the eifective width of the chamber may be readily adjusted by turning the cylindrical insulating chamber wall I22 by means of its grip holes I25 on its threads I2I to bring the stationary carbon plate I21 nearer or farther away from the diaphragm carbon electrode I25 and thus vary the effective normal pressure under which the carbon ball filling within the vertical chamber is held.

Figs. 11 and 12 illustrate another exemplification of a hearing-aid microphone amplifier unit of the invention. It comprises a casing having a base plate I40 of suitable-insulating material shaped to fit and rest with its ridges on the top of the battery and provided at one end with a vertical microphone mounting wall MI and at its other end with a terminal ridge I42. In the space between the wall I4! and the terminal ridge I42 is mounted a rectangular supporting block I45, of brass, for instance, which is suitably secured to the base plate by means of screws I45.

Within a cylindrical cavity I48 of the block I facing the terminal ridge is mounted the core structure of the vibrating unit comprising a permanent magnet ring l5Il magnetized in diametrical direction and-two L-shaped pole pieces I5I held clampedin place by a clamping ring I52 having a threaded exterior engaging a threaded portion of the cavity wall. The opposite side of the supporting block I45 is provided with a larger cylindrical cavity I54 which is accessible through a conical wall opening I55 within the vertical casing wall I iiextending' from the" amplifier base I45.

Into the large-block cavity I54 and the wall opening I55 fits a readily detachable amplifier microphone unit I comprising a conical wall member I5I of insulating .material, such as a molded synthetic resin, provided with an extension I62 constituting the wall of *the chamber cavity. A supporting ring I64, of brass, for instance, suitably secured to the wall member I6I, as in the molding operation, is provided with an inwardly projecting annular seating ridge I65, to which is clamped, over a spacing washer I66, the periphery of a circular spring diaphragm I61 by means of a clamp ring-l68 having a cylindrical threaded portion engaging a corresponding cylindrical threaded portion of the outer surface of thesupp'orting ring I64.

- T o'the center portion of the diaphragm I61 facing the pole pieces I5I is attached a magnetic armature I 10 which completes the magnetic path between the pole pieces'I5I. To the side of the diaphragm I61 opposite'the chamber opening is secured a circular carbon electrode I69 shaped to prevent loose carbon balls I12 from dropping out from the microphone chamber I62 when the armature vibrates. I

I on the side of the microphone chamber I62 opposite the diaphragm electrode I59, the carbon balls I12 in the microphone chamber are in engagement'with a carbon electrode I14 which is attached to a supporting disc I15 having a threaded periphery engaging a threaded portion of the enclosing chamber wall I62 to permit adjustable fixing of the position of the electrode I14 relatively to the diaphragm electrode I59, a small normally plugged-up hole I16 in the outer chamber wall I6I permitting the insertion of a screw driver into a slot in the supporting disc I15 for turning the disc with its electrode member I14 to the desired position in the chamber I62.

The conical seating surface of the wall I6I which engages the conical seat I of the projecting amplifier casing wall MI is provided with a sealing ring I19 of suitable resiliently yielding, electrically conduction material, such as copper or phosphor bronze, so that when the microphone unit is mounted on its threaded supporting connection within the cylindrical block cavity I54 in the way shown in Fig. 11, the seating ring I49 which is connected through a conducting strip I embedded in the insulating wall I6I and a conducting spring washer I8I to the microphone electrode I14 completes a conducting connection to the contact spring mounted on the casing base I40, which in turn leads to one of the terminal sockets which is engaged by the terminal plug pin of the receiver lead.

The magnetic unit with the supporting block of the amplifier casing is enclosed by a detachable cover I which is secured to the block by screws I85. The various elements of the amplifier unit enclosed in the casing are suitably connected to the two battery'plugs I9I and I92 mounted on the casing base and to the three socket terminals I93, I94, I95 mounted in the terminal ridge I 42 in the way shown diagrammatically in Fig; 1 and explained in connection with the exemplification of Figs. 2 to 6.

With such hearing-aid amplifier arrangement, the self-contained microphone unit I60 may be readily removed from the amplifier casing by unscrewing it by means of the grip holes I98 from its threaded seat in the block cavity which is engaged by the threaded portion of the supporting ring I64 and readily replaced by another similar unit. Thus, a hearing-aid in which the amplifier was rendered defective by excessive burning or other form of deterioration after a certain period of use may be quickly reconditioned by simply unscrewing the self-contained microphone unit from the wall of the amplifier casing and replacing it quickly with a good amplifier microphone unit. Since the response characteristics of microphone amplifiers are determined by the design of the diaphragm electrode, the response of a microphone amplifier of the invention may be selectively determined by merely replacing an amplifier microphone unit of a given response characteristic with another amplifier microphone unit of a diiierent predetermined response characteristic. As a result, the problem of selective fitting of hearing-aids or audiphones may be simplified by providing sets of readily interchangeable amplifier microphone units of different response characteristics, and testing the hearing-aid assembly equipped with a microphone amplifier of the invention while'successively replacing one amplifier microphone unit with another of different response characteristics until the combination which gives the individual best hearing is determined.

In fitting an audiphone provided with a microphone amplifier of the invention, several amplifier microphones having different response characteristics are successively placed in their operative position on the vibratory amplifier structure and the hearing of the user is tested while he hears through the audiphone operating with each of the different amplifier microphone units to determine which of the combinations of one of the several amplifier microphones with said audiphone gives the user the best hearing.

The principles of the invention disclosed in connection with the exemplification described abovewill suggest many other modifications of the invention. It is accordingly desired that the appended claims be given a broad construction commensurate with the scope of the invention.

We claim:

1. In a wearable microphone amplifier actuated by speech-frequency input currents supplied through an input circuit for producing corresponding amplified currents delivered to an output circuit of a wearable hearing aid device, or the like, an amplifier microphone comprising a microphone chamber, a vibratory microphone electrode of one polarity facing the interior of said chamber, a microphone electrode of opposite polarity facing the interior of said chamber, and a quantity of microphone granules held in said chamber by said vibrat'ory microphone electrode so as to produce variations of the currents in said output circuit in response to the vibratory motion imparted to said granules by said vibratory electrode, a vibratory structure including a magnetic core having windings actuated by said input currents for imparting a vibratory motion to said vibratory electrode throughout the principal speech frequency range, said vibratory electrode having a magnetic armature portion constituting with said magnetic core a low reluctance magnetic path including agap, a holding member, holding said vibratory structure and the associated amplifier microphone in their operative positions while worn on the body of the user, said holding member having a plurality of insulatingly held connectors for establishing circuit interconnections from the elements of said vibratory structure and said amplifier microphone electrodes to said input and output circuits, said microphone chamber and said two microphone electrodes constituting, a selfcontained microphone unit of predetermined dimensions detachably held on said holding member in fixed operative relation to said vibratory structure so as to permit removal and exchangeable replacement of said microphone unit Without interrupting the interconnections between said connector elements and said output and input circuits and without disturbing the operative relations of the elements of said microphone amplifier.

rents in said output circuit in response to the vibratory motion imparted to said granules by said vibratory electrode, a vibratory structure including a-magnetic core having windings actuated by said input currents for imparting a vibratory motion to said vibratory electrode through- I out the principal speech frequency range, said vibratory electrode having a magnetic armature portion constituting with said magnetic core a low reluctance 'magnetic path including a gap,

a holding member holding said vibratory struc- I ture and the associated amplifier microphone in their operative positions while worn on the body of the user, said holding member having a plurality of insulatingly held connectors for establishing circuit interconnections from the elements of said vibratory structure and said amplifier microphone electrodes to said input and output circuits including a circuit connection from said microphone electrode of opposite polarity to said output circuit, said microphone chamber and said two microphone electrodes constituting a self-contained microphone unit of predetermined dimensions detachably held on said holding member in fixed operative relation to said vibratory structure so as to permit removal and exchangeable replacement of said microphone unit without interrupting the interconnections between said connector elements and said output and input circuits and without disturbing the operative relations of the elements of said microphone amplifier.

3. In a wearable microphone amplifier actuated by speech-frequency input currents supplied through an input circuit connected to a battery for producing corresponding amplified currents delivered to an output circuit of a wearable hearing aid device, or the like, an amplifier microphone comprising a micro-phone chamber, a vibratory microphone electrode of one polarity facing the interior of said chamber, a microphone electrode of opposite polarity facing the interior. of said chamber, and a quantity of microphone granules held in said chamber by said vibratory microphone electrode so as to produce variations of the currents in said output circuit in response to the vibratory motion imparted to said. granules by said vibratory electrode, a vibratory structure including a magnetic core having windings actuated by said input currents for imparting a vibratory motion to said vibratory electrode throughout the principal speech frequency range, said vibratory electrode having a magnetic armature portion constituting with said magnetic core a low reluctance magnetic path including a gap, a holding member holding said vibratory structure and the associated amplifier microphone in their operative positions while worn on the body of the user, said holding member having a plurality of insulatingly held connectors for establishing circuit interconnections from the elements of said vibraelectrodes to said input and output circuits including acircuit connection from said microphone electrode of opposite polarity to said output circuit, at least one of said connectors constituting a detachable junction mechanically supporting said holding member on said battery, said microphone chamber and said two microphone electrodes constituting a self-contained microphone unit of predetermined. dimensions detachably held on said holding member in fixed operative relation to said vibratory structure so as to permit removal and exchangeable replacement of said microphone unit without interrupting the interconnections between said connector elements and said output and input circuits and without disturbing the operative relations of the elements of said microphone amplifier.

4. In a wearable microphone amplifier actuated by speech-frequency input currents supplied through an input circuit for producing corresponding amplified currents delivered to an output circuit of a wearable hearing aid device, or the like, an amplifier microphone comprising a microphone chamber, a vibratory microphone electrode of one polarity facing the interior of said chamber, a microphone electrode of opposite polarity facing the interior of said chamber, and a quantity of microphone granules held in said chamber by said vibratory microphone electrode so as to produce variations of the currents in said output circuit in response to the vibratory motion imparted to said granules by said vibratory electrode, a vibratory structure including a magnetic core having windings actuated by said input currents for imparting a vibratory motion to said vibratory electrode throughout the principal speech frequency range, said vibratory electrode having a magnetic armature portion constituting with said magnetic core a low reluctance magnetic path including a gap, a casing enclosing and holding said vibratory structure and the associated amplifier microphone in their operative positions while worn on the body of the user, said casing having a plurality of insulatingly held connectors for establishing circuit interconnections from the elements of said vibratory structure and said amplifier microphone electrodes to said input and output circuits including a circuit connection from said microphone electrode of opposite polarity to said output circuit, said micro-phone chamber and said two microphone electrodes constituting a self-contained microphone unit of predetermined dimensions detachably held in said casing in fixed operative relation to said vibratory structure so as to permit removal and exchangeable replacement of said microphone unit without interrupting the interconnections between said connector elements and said output and input circuits and without disturbing the operative relations of the elements of said microphone. amplifier. 1

5. In a wearable microphone amplifier actuated by speech-frequency input currents supplied through an input circuit connected to a battery for producing corresponding amplified currents delivered to an output circuit of a wearable hearing aid device, or the like, an amplifier microphone comprising a microphone chamber; a vibratory microphone electrode of one polarity facing the. interior of said chamber, a microphone I electrode of opposite polarity facing the interior of said chamber, and a quantity of microphone tory structure and said amplifier microphone granules held in said chamber by said vibratory microphone electrode so as to produce variations of the currents in said output circuit in response to the vibratory motion imparted to said granules by said vibratory electrode, a vibratory structure including a magnetic core having windings actuated by said input currents for impartin a vibratory motion to said vibratory electrode throughout the principal speech frequency range, said vibratory electrode having a magnetic armature portion constituting with said magnetic core a low reluctance magnetic path including a gap, a casing inclosing and holding said vibratory structure and the associated amplifier microphone in their operative positions while Worn on the body of the user, said casing having a plurality of insulatingly held connectors for establishing circuit interconnections from the elements of said vibratory structure and said amplifier microphone electrodes to said input and output circuits including a circuit connection from said microphone electrode of opposite polarity to said output circuit, at least one of said connectors constituting a detachable junction mechanically supporting said casing on said battery, said microphone chamber and said two microphone electrodes constituting a self-contained microphone unit of predetermined dimensions detachably held in said casing in fixed operative relation to said vibratory structure so as to permit removal and exchangeable replacement of said microphone unit without interrupting the interconnections between said connector elements and said output and input circuits and without disturbing the operative relations of the elements of said microphone amplifier.

6. In a wearable microphone amplifier actuated by speech-frequency input currents supplied through an input circuit for producing correof one-polarity facing the interior of said chamber, a microphone electrode of opposite polarity facing the interior of said chamber, and a quantity of microphone granules held in said chamber by said vibratory microphone electrode so as to produce variations of the currents in said output circuit in response to the vibratory motion imparted to said granules by said vibratory electrode, a vibratory structure including a magnetic core having windings actuated by said input currents for imparting a vibratory motion to said vibratory electrode throughout the principal speech frequency range, said vibratory electrode having a magnetic armature portion constituting with said magnetic core a low reluctance magnetic path including a gap, a casing enclosing and holding said vibratory structure and the associated amplifier microphone in their operative positions while worn on the body of the user, said casing having a plurality of insulatingly held connectors for establishing circuit interconnections from the elements of said vibratory structure and said amplifier microphone electrodes to said input and output circuits including a circuit connection from said microphone electrode of oppositepolarity to said output circuit, said microphone chamber and said two microphone electrodes constituting a self-contained microphone unit of predetermined dimensions forming a wall portion of said casing detachably held in said casing in fixed operative relation to said vibratory structure so as to permit removal and exchangeable replacement of said microphone unit without interrupting the interconnections between said connector elements and said output and input circuits and without disturbing the operative relations of the elements of said microphone amplifier.

7 The method of determining the response characteristics of a microphone amplifier forming a part of a hearing aid device for a hard of hearing person, which comprises providing a microphone amplifier having a vibratory amplifier structure actuated by input currents and a set of several self-contained amplifier microphone units of predetermined different audible frequency response characteristics for supplying amplified output currents for the hearing aid device, and successively testing the microphone amplifier with each amplifier microphone unit having a difierent frequency response for determining which combination of one of said amplifier microphone units with said vibratory amplifier structure gives to said audiphone an overall response characteristic which suits best to the person.

8. The method of determining the response characteristics of a microphone amplifier forming a part of a hearing aid device for a hard of hearing person, which comprises providing a microphone amplifier having a vibratory amplifier structure actuated by input currents and a set of several self-contained amplifier microphone units of predetermined different audible frequency response characteristics in the speech freguency range for supplying amplified output currents for the hearing aid device, and successively testing the microphone amplifier with each amplifier microphone unit having a different frequency response for determining which combination of one of said amplifier microphone units with said vibratory amplifier structure gives to said hearing aid device an" overall response characteristic which suits best to the person.

9. In an arrangement for fitting a hearing aid having an input circuit including a transmitter microphone having certain response characteristics and an output circuit including a hearing inducing receiver having certain response characteristics, a microphone amplifier comprising a holding member having a plurality of insulatingly held connectors for establishing circuit connections from the elements of said microphone amplifier to said input and output circuits, a driving structure mounted on said holding member and including actuating windings energized by speechfrequency currents from said transmitter, and a set of a plurality of self-contained amplifier microphones, each having a body of contact granules and a vibratory diaphragm arranged to impart vibratory forces to said granules for supplying amplified currents to said receiver when actuated by said driving structure; each of said amplifier microphones differing from each of the other amplifier microphones in its response characteristics; and each of said amplifier microphones being designed to be interchangeably mounted on said holding member in operative relation to said driving structure for enabling selective determination of the particular amplifier microphone which will in conjunction with said driving structure, said transmitter, and said receiver supply to the user sound energy having an overall frequency response which fits best his needs.

10. In an arrangement for fitting a hearing aid having an input circuit including a transmitter microphone having certain response characteristics and an output circuit including a hearing inducing receiver having certain response characteristics, a microphone amplifier comprising a casing having a plurality of insulatingly held connectors for establishing circuit connections from the elements of said microphone amplifier to said input and output circuits, 9. drivin structure mounted within said casing and including a magnetic pole piece and actuating windings interlinked with said pole piece energized by speech-frequency currents from said transmitter, and a set of a plurality of self-contained amplifier microphones, each having a body of contact 7 granules and a vibratory diaphragm including an armature arranged to impart vibratory forces to said granules for supplying amplifier currents to said receiver when said armature is actuated by the pole piece of said driving structure; each of said amplifier microphones diifering from each of the other amplifier microphones in its response characteristics; and each of said amplifier microphones being designed to be interchangeably mounted within said casing in operative relation to said driving structure for enabling selective determination of the particular amplifier microphone which will in conjunction with said driving structure, said transmitter, and said receiver supply to the user sound energy having an overall frequency response which fits best his needs.

DEAN BABBITT. HERMANN SCHEIBLER. 

